DESCRIPTION: The proposal aims to identify mechanisms to help explain why there is such a high prevalence of obesity in black women. It tests the following hypotheses: that black women compared to white women have greater predisposing factors to obesity, including a lower energy expenditure and resting fat oxidation, a relative failure to appropriately increase fat oxidation in response to a high fat diet or to exercise, a lower proportion of Type I muscle fibers, a lower activity of muscle lipoprotein lipase and a higher activity of adipose tissue LPL. Further they hypothesize that compared to subcutaneous adipocytes, mental adipocytes from black women are smaller and don't show high metabolic activity as assessed by adrenergic regulation and sensitivity to the antiipolytic effects of insulin. The proposal has three experiments, the first will compare glucose tolerance, energy expenditure, substrate utilization, nutrient oxidation and storage, muscle morphology, and adipocyte metabolism in 96 lean and obese black and white women in response to an AHA and a high fat diet. The second experiment will study metabolism of abdominal adipocytes in 40 black and white obese women undergoing routine gynecologic surgeries to measure lipolysis, insulin and adrenergic response, LPL, triglyceride syntheses and aspects of glucose metabolism. the third study will assess effect of catacolamines in 20 white and black obese women by an IV infusion protocol in which fatty acid and glycerol turnover, and glucose metabolism and disposal will be measured in response to epinephrine at three different concentrations (a sort of epinephrine dose response clamp).